Process for refining soybean oil



Patented July 24, 1951 PROCESS FOR REFINING SOYBEAN OIL Arnold L. Ayers, Bartlesville, kla., asslgnor to Phillips Petroleum Company, a corporation of Delaware No Drawing. Application March 25, 1948, Serial N0. 17,105

This invention relates to the treatment of soybean oil. In one of its more specific aspects, it relates to an improved process for refining soybean oil. In one specific embodiment, this invention relates to a process for refining crude soybean oil to obtain an oil substantially free of impurities which may be employed as a film forming constituent in paints, varnishes, enamels, synthetic resins, as food products, drug products, in soaps, plastics, and the like.

Soybean oil is customarily extracted from the seed meal either by application of high pressure or by extraction with a suitable solvent such as n-hexane. It is a characteristic of these processes that other minor components, although often valuable and desirable within themselves, are removed with and are undesirable in the oil. For example, in either the pressing operation or solvent extraction with a hydrocarbon solvent, 0.5 to 1.0 per cent of phosphatides and 1 to 2 per cent free fatty acids are usually obtained in the extracted oils. In addition, certain materials which seem to exert an antioxidant effect upon drying oils are often obtained which render the oil less satisfactory for use in paints, varnishes, etc., although not for food usage. In the paint and varnish industries, it is particularly desirable to remove those portions of the oil which cause so-called break or sludge formation upon heating and to remove excess free fatty acids, color bodies, and non-drying constituents from the oil.

One conventional method of refining these oils involves the use of large volumes of concentrated sodium hydroxide or other harsh reagents which often tend to char and coagulate the by-products of the oil. Such a method is drastic in its action upon the oil, frequently destroying certain constituents entirely, and leaving by-products which have little or no value. In addition to causing destruction or degradation of the by-products, such treatment also tends to decompose a part of the drying or film-forming oils. A method such as this is tedious and usually requires considerable investment in equipment, and much space for storage purposes. Furthermore, the reagents employed in the process are not recoverable, and along with the by-products which are obtained in a degraded form, constitute a considerable source of economic loss.

An object of this invention is to provide an improved process for treating soybean oil. Another object is to provide an improved method for refinin crude soybean oil. Another object is to remove from soybean oil components which may be undesirable for the use to which the oil is to be put. Another object is to product soy- 7 Claims. (Cl. 260-426) bean oil of high purity. Another object is to provide an extraction process for purifying soybean oil. A further object is to provide a twostage liquid-liquid extraction process for producing high purity soybean oil. Other objects and advantages of this invention will be apparent to one skilled in the art from the following disclosure and discussion.

. The term miscella as used in this specification describes a mixture of soybean oil, the solvent-extracting material, and any impurities extracted from the soybean along with the oil. It is used to include also merely a mixture of soybean oil and solvent after undesirable impurities I have been removed.

The break materials as referred to herein I consist principally of phosphatides, color bodies,

and mucilaginous materials. They are measured by the Gardner method which consists of the following: Three drops of hydrochloric acid are added to 25 grams of oil and the mixture heated to 550 F. The oil sample is cooled and dissolved in carbon tetrachloride, and the remaining break (undissolved residue) is filtered, dried, and weighed.

I have discovered an improved two-stage process for the purification of crude soybean oil, wherein undesirable components of the oil are efliciently removed by liquid-liquid extraction from an oil-hydrocarbon solvent miscella with aqueous methanol followed by a dilute aqueous solution of an alkali metal hydroxide, such as sodium or potassium hydroxide.

My invention pertains to the treatment of soybean oil removed from the bean either by solvent extraction or by squeezing the bean, thus pressing out the oil. When oil obtained by this latter method is to be treated, it must first have from 1 to 4 volumes of the hydrocarbon solvent, described herein, added to it. In a preferred embodiment of my invention soybean oil is extracted from the bean with normal hexane. This miscella of crude soybean oil and normal hexane containing from 1 to 4 volumes of normal hexane per volume of extracted oil is contacted in liquid phase at a temperature in the range of -20 to C. and preferablyin the range of 0 to 30 C. with a methanol-water solution containing from 0 to 25 volume per cent water, but preferably from 5 to 15 volume per cent. (The higher the temperature in this step, the more water required.) A suitable proportion by volume of the methanol water solution to the soybean oil miscella is in the range of 1:1 to 1:30, however, the preferred ratio is 1:5 to 1:15. .The miscellamethanol-water mixture is agitated for a period of time sufficiently long to insure adequate contact oi the components. A suitable contact time is usually 5 minutes or longer and preferably be-- tween 5 and 10 minutes. After contacting for a sufficient time, the methanol-water solution is separated by suitable means, such as settling. This step of my process removes break materials comprising color bodies, phosphatides, mucilaginous materials, non-drying materials, and the like. When it is desirable to recover the break materials, phosphatides, etc. from the methanol-water extracting solution, it may be done by such means as evaporation as reduced pressure or by any other suitable means.

Follo ing the separation of the methanolwater solution from the miscella, a dilute aqueous solution of sodium hydroxide or other alkali metal hydroxide, preferably a solution containing from 1 to 5 weight per cent of the hydroxide, is added to the methanol-water extracted soybean oil-normal hexane miscella at a temperature in the range of to 130 C., but preferably in the range of 0 to 30 C. Preferably from to volumes of the hydroxide solution are used per each 100 volumes of miscella to be treated. The mixture is agitated for a suitable period of time, preferably for 5 minutes or longer. After the agitation, the mixture is allowed to settle and the aqueous hydroxide solution withdrawn, thus removing the fatty acids.

After the hydroxide solution has been separated from the miscella, the normal hexane is removed by suitable means, such as distillation, steam stripping, and the like. This leaves the oil in condition for marketing. It has an improved color (as much as three points on the Gardner scale) and is bland in taste and odor.

My process may be practiced either batchwise or continuously. In a. continuous operation, the miscella is contacted countercurrently in a suitable extraction column with the methanol-water solution. The mixture of higher specific gravity is introduced in the upper zone and that of lower specific gravity in the lower zone. The miscella may be recovered overhead if it is of lower specific gravity and passed to another extraction column where it is similarly treated with the dilute solution of an alkali metal hydroxide. In either batchwise or continuous operation, it is necessary to use equipment which may be maintained at the required temperature, pressure, etc.

While the description of the above embodiment was restricted to the treatment of a soybean oil dissolved in normal hexane, my invention is not to be limited to treatment of the oil in this solvent. Other hexanes such as diisopropyl and neohexane are often used for oil extraction with great advantage and this process may be applied to such miscella with equal facility. Pentanes, heptanes, and other hydrocarbons are also used and their miscella may also be treated by my process. Such solvents may be used either in a rather pure state or as refinery cuts which contain certain impurities. The use of mixtures of .the above solvents is also within the scope of the invention.

Advantages of my invention are illustrated by the following examples. The reactants and their proportions, and other specific ingredients are presented as being typical and should not be construed to limit the invention unduly.

Example I Fifty ml. (milliliters) of a normal hexanesoybean oil miscella containing solvent and oil in a ratio by volume of approximately 3.521 was agitated for 5 minutes in the presence of 5 ml. or methanol containing 8 volume per cent water.

. At the end of the agitation period, the heavier methanol-water phase was allowed to settle and was withdrawn. Five ml. of a 2 weight per cent aqueous sodium hydroxide solution was then added to the miscella, agitated for 5 minutes, allowed to settle, and was withdrawn. The bulk of the normal hexane was flashed from the oil by ordinary distillation at atmospheric pressure. Residual solvent was removed under vacuum at a pressure of 15 mm. of mercury. The oil temperature was never allowed to rise above 0.; this limit being observed to reduce the possibility of thermal decomposition. Eleven ml. of purifled oil was recovered. The properties of this oil are compared with those of the crude normalhexane-extracted oil in the following data:

Approximate refining 1055. 0.9%.

Example I! Fifty ml. of a diisopropyl (2,3-dimethyl butane) extracted soybean oil miscella containing solvent and oil in a volume ratio of approximately 4:1 were treated according to the process of Example I. The properties of the refined oil are compared with those of the crude diisopropylextracted oil.

Gardner Free Fatty Break A cid Sample (Weight (Weight per cent per cent of Oil) of Oil) Untreated oil from diisopropyl miscella 0. 38 1+ Refined oi] 0. l4 0.00

Example HI Fifty ml. of a neohexane (2,2-dimethyl butane) -soybean oil miscella was treated according to the process of Example I. The properties of the refined oil arecompared with those of crude neohexane-extracted oil.

Gardner Free Fatty Break Acid Sample (Weight (Weight per cent per cent of Oil) of Oil) Untreated oil from neohexane miscella.. 0. 29 1+ Refined oil 0. 15 0.00

From the foregoing disclosure it may be seen that soybean oil may be refined by my process in such a manner that neither the product oil nor the by-product impurities are damaged by the extraction process. Another advantage of my process is that the break" materials comprising color bodies, phosphatides, and the like are readily removed from the methanol-water solution and may form an added source of income to the processor. A further advantage is economy of operation by reusing the methanol-water extracting solution. An additional advantage of my process is a reduction in refining losses by having the oil dissolved in a solvent, thus reducing foam and emulsion formation, which normally are responsible for considerable loss. A further advantage is that the soybean meal which is left after the oil has been extracted by the hydrocarbon is suitable for feed purposes, because there is no toxic methanol present as is the case in some other processes.

Although this process has been described and exemplified in terms of its preferred modifications, it is understood that various changes may be made without departing from the spirit and and scope of the disclosure and of the claims.

I I claim:

1. An improved process for refining crude soybean oil, which comprises extracting soybean oil from the bean with from 1 to 4 volumes of normal hexane per volume of oil to be extracted, intimately contacting in liquid phase at a temperature in the range of to 30 C. and for a period of time within the range of 5 to minutes the resulting crude soybean oil-normal hexane miscella and a methanol-water solution containing 5 to volume per cent water in a volume ratio of said solution to said miscella of 1:5 to 1:15 and thereby extracting color bodies, phosphatides, mucilaginous materials, and non-drying materials from said oil, separating said methanol-water solution containing extracted materials from said miscella, intimately contacting said miscella in liquid phase at a temperature in the range of 0 to 30 C. and for a period of time of at least 5 minutes with an aqueous solution of sodium hydroxide containing from 1 to 5 weight per cent sodium hydroxide in a ratio of 5 to 10 volumes of said aqueous solution per 100 volumes of miscella and thereby extracting fatty acids from said oil, separating said sodium hydroxide solution containing said fatty acids from said miscella, and separating said normal hexane from said soybean oil and thereby producing purified soybean oil as a product of the process.

2. An improved process for refining crude soybean oil, which comprises extracting soybean oil from the bean with from 1 to 4 volumes of normal hexane per volume of oil to be extracted, intimately contacting in liquid phase at a temperature in the range of to 130 C. and for a period of time of at least 5 minutes the resulting soybean oil-normal hexane miscella and a methanol-water solution containing 0 to volume per cent water in a volume ratio of said solution to said miscella of 1:5 to 1:15 and thereby extracting color bodies, phosphatides, mucilaginous materials, and non-drying materials from said oil, separating said methanol-water solution containing extracted materials from said miscella, intimately contacting said miscella in liquid phase at a temperature in the range of 0 to 130 C. and for a sufiicient time to remove fatty acids with an aqueous solution of sodium hydroxide containing from 1 to 5 weight per cent sodium hydroxide in a ratio of 5 to 10 volumes of said aqueous solution per 100 volumes of miscella, separating said sodium hydroxide solution containing said fatty acids from said miscella and separating said normal hexane from said soybean oil and thereby producing purified soyban oil as a product of the process.

3. An improved process for producing purified soybean oil, which comprises forming a miscella of soybean oil and normal hexane, intimately contacting the resulting soybean oilnormal hexane miscella and a methanol-water fatty acids from said oil, separating said sodium hydroxide solution containing said fatty acids from said miscella, and separating said normal hexane from said soybean oil and thereby producing purified soybean oil as a product of the process.

4. The process according to claim 3 wherein soybean oil is extracted from soybeans by the addition of normal hexane and thereby forming a miscella of soybean oil and normal hexane.

5. The process according to claim 3 wherein normal hexane is added to liquid soybean oil and thereby forming a miscella of soybean oil and normal hexane.

6. An improved process for producing purified soybean oil, which comprises forming a miscella of soybean oil and a hexane, contacting the resulting soybean oil-hexane miscella with a methanol-water solution and thereby extracting impurities from said 011, separating said methanol-water solution containing said extracted impurities from said miscella, contacting said miscella with a dilute aqueous solution of an alkali metal hydroxide and thereby extracting fatty acids from said oil, separating said alkali metal hydroxide solution containing said fatty acids from said miscella, separating said hexane from said soybean oil, and recovering a purified soybean oil as a product of the procass. 1

7. An improved process for producing purified soybean oil, which comprises forming a miscella of soybean oil and a suitable paraflin hydrocarbon solvent, contacting the resulting soybean oil-hydrocarbon miscella and a methanol-water solution and thereby extracting impurities from said miscella, separating said methanol-water solution containing said impurities from said miscella, contacting said miscella with a minor portion of an alkali metal hydroxide and thereby extracting fatty acids from said 011, separating said alkali metal hydroxide containing said fatty acids from said miscella, separating said paraffin hydrocarbon solvent from said soybean oil and recovering a purified soybean oil as a product of the process.

ARNOLD L. AYERS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,069,187 Kraybill Jan. 26, 1937 2,396,681 Buxton Mar. 19, 1946 2,461,750 Marmor Feb. 15, 1949 FOREIGN PATENTS Number Country Date 402,265 Germany Sept. 1886 OTHER REFERENCES Horvath, Soybean Industry (1938), Chemical Pub. C0" Pp. 77-78. 

6. AN IMPROVED PROCESS FOR PRODUCING PURIFIED SOYBEAN OIL, WHICH COMPRISES FORMING A MISCELLA OF SOYBEAN OIL AND A HEXANE, CONTACTING THE RESULTING SOYBEAN OIL-HEXANE MISCELLA WITH A METHANOL-WATER SOLUTION AND THEREBY EXTRACTING IMPURITIES FROM SAID OIL, SEPARATING SAID METHANOL-WATER SOLUTION CONTAINING SAID EXTRACTED IMPURITIES FROM SAID MISCELLA, CONTACTING SAID MISCELLA WITH A DILUTE AQUEOUS SOLUTION OF AN ALKALI METAL HYDROXIDE AND THEREBY EXTRACTING FATTY ACIDS FROM SAID OIL, SEPARATING SAID ALKALI METAL HYDROXIDE SOLUTION CONTAINING SAID FATTY ACIDS, FROM SAID MISCELLA, SEPARATING SAID HEXANE FROM SAID SOYBEAN OIL, AND RECOVERING A PURIFIED SOYBEAN OIL AS A PRODUCT OF THE PROCESS. 